How can i generate a function using this points?

If i got x=[1,3,8,25,45,23]; and y=[25,24,13,69,25,75];

[Adam]

What do you expect the function to do exactly?! Handle exactly that one input, returning that one output and throw an error or crash if you give it any other input?

Or do you mean you want to plot these points as x against y?

[Mr. 206]

This is an example where there is a y function depends on the values of x. I don't have such function, i only have points so i want a function so that i can use it for example in the below code.

% Simple curve
  x = linspace(0,100,200);
   y = cos(x/10)+(x/50).^2 + randn(size(x))/10;
   z = smooth1q(y,[]);
   plot(x,y,'r.',x,z,'k','LineWidth',2)
%   axis tight square

[Adam]

There are an infinite number of functions that could take that one example input and give that output.

[Mr. 206]

Okey for example if i want a polynomial function, can you help me?

Answer 1

[Jan]

x = [1,3,8,25,45,23];
y = [25,24,13,69,25,75];
p = polyfit(x, y, 5)

Answer 2

[Cesar Antonio Lopez Segura]

Hi Here the solution:

% Your cloud point
x=[1,3,8,25,45,23]; 
y=[25,24,13,69,25,75];
% calculate a new cloud point that contain the last one
xnew = [1, 1.5 ,3,6,8,25,32,45,31,23];
ynew = interp1( x,y, xnew,'pchip' );
% plot de new values
plot(x,y,'o');hold on;plot( xnew, ynew,'r' )
% polinomios
p = interp1( x,y,'pchip' );

[Mr. 206]

Thanks for reply. Using this 'pchip' command gives an error "error: interp1: discontinuities not supported for method 'pchip'"

[Cesar Antonio Lopez Segura]

What is your MATLAB version ?

Your cloud point

x=[1,3,8,25,45,23];  y=[25,24,13,69,25,75];
[xtointerpol indx ] = sort(x);
ytointerpol = y(indx);
% calculate a new cloud point that contain the last one
ynew = interp1( xtointerpol,ytointerpol, xtointerpol, 'pchip' );
% plot de new values
close all
% plot(x,y,'+b');hold on;plot( xnew, ynew,'--or' )
 plot(x,y,'+b');hold on;
 plot( xtointerpol, ynew,'--or' )
% polinomios
p = pchip( xtointerpol,ytointerpol );

[Mr. 206]

Great, Now it is working. Thanks :)

[Mr. 206]

If the x values are not monotonic, then is there any way to handle this?

[Cesar Antonio Lopez Segura]

You can define x values in ascending order with sort.

Then you can order de y values.

[xtointerpol indx ] = sort(x);
ytointerpol = y(indx);